1. Field of the Invention
The present invention relates to an apparatus and method for receiving a digital broadcasting service, and, in particular, to an apparatus and method for receiving broadcasting data in a digital video broadcasting receiver using the Digital Video Broadcasting-Handhelds (DVB-H) standard.
2. Description of the Related Art
Generally, broadcasting services are provided to all users with terminals. These broadcasting services are classified into an audio broadcasting service such as radio broadcasting service for providing only audio, a video broadcasting service such as television for providing audio and video services, and a multimedia broadcasting service including audio, video, and data services. The broadcasting services are based on an analog system, and are currently evolving into digital broadcasting with the rapid development of various technologies. Moreover, the broadcasting services are being developed in various systems such as a multimedia service system of a wired network for providing data of high image quality at high rates by wire, a system for providing a multimedia service using an artificial satellite, and a system that simultaneously uses a wire and an artificial satellite, without use of a system for providing a service on the basis of a transmission tower conventionally managed by a broadcasting station.
Recently, a Digital Multimedia Broadcasting (DMB) system, as one of the above-described systems, is being actively commercialized. This DMB system has been derived from Digital Audio Broadcasting (DAB) and is based on European Research Coordination Agency (Eureka) Project-147, serving as the technical standard of DAB in Europe.
In Europe, as the origin of the DAB technology, a group called Digital Video Broadcasting (DVB) has been organized for multimedia broadcasting services and is working to establish a separate standard for portable broadcasting services, called Digital Video Broadcasting-Handhelds (DVB-H). DVB-H is a new broadcasting standard under development by Digital Audio Broadcasting (DAB) that is a European Group for digital TV broadcasting standardization, following satellite digital TV (DVB-S), digital cable TV (DVB-C), and terrestrial digital TV (DVB-T).
The determination that voluminous multimedia contents such as movies or broadcast dramas cannot be implemented through portable terminals in accordance with 3rd mobile communication (Universal Mobile Telecommunication System (UMTS) or International Mobile Telecommunications-2000 (IMTS-2000)), terrestrial digital TV, and DAB, the DVB group has promoted standardization named ‘DVB-extension (DVB-X)’, which was later renamed DVB-H to clearly indicate ‘portable broadcasting’.
DVB-H is designed to reinforce mobility in the European digital TV transmission standard DVB-T and is an extension of DVB-T considering low power, mobility, and portability of mobile terminals or portable video devices. Thus, most physical layer standards of DVB-H comply with those of DVB-T and several functions for portable/mobile reception are added thereto.
DVB-H systems support additional Error Correction Coding (ECC) for layer-3 Internet Protocol (IP) packets. This additional ECC process is called Multi Protocol Encapsulation—Forward Error Correction (MPE-FEC).
In DVB-H systems, broadcasting data is composed of IP datagrams and an MPE-FEC frame is formed by performing Reed-Solomon (R-S) coding on the IP datagram. Thus, the MPE-FEC frame is composed of an MPE section carrying the IP datagram and an MPE-FEC section carrying parity data resulting from the R-S encoding. The MPE section and the MPE-FEC section are transmitted through a payload of a Transport Stream (TS) packet, which is a transport unit of the DVB-H system, over a physical layer.
FIG. 1 illustrates the data structure of a TS packet in a general DVB-H system. Referring to FIG. 1, reference numeral 100 indicates an IP datagram that carries broadcasting data or application data. The datagram means a packet including the address of a network termination point to which data is destined. Reference numeral 102 indicates an MPE section carrying the IP datagram 100 or an MPE-FEC section carrying parity data of the IP datagrams 100. Reference numeral 104 indicates a TS packet carrying the MPE section or MPE-FEC section 102. A single TS packet 104 may include a plurality of MPE sections or MPE-FEC sections 102 or a single MPE section or MPE-FEC section 102 may be transmitted through a plurality of TS packets 104.
FIG. 2 explains R-S encoding performed by a transmitter of a general DVB-H system. The transmitter generally performs a single R-S encoding operation in each of a physical layer and a link layer. Referring to FIG. 2, reference numeral 200 indicates a column of an MPE-FEC frame and reference numeral 202 indicates a row of the MPE-FEC frame. The column 200 is composed of 255 bytes, in which a left region of 191 bytes is an application data table region 204 for the MPE section including the IP datagram 100 and a right region of 64 bytes is an R-S data table region 206 for R-S data or parity data resulting from R-S encoding with respect to broadcasting data stored in the application data table region 204. In contrast, the row 202 is variable up to 1024 rows.
As illustrated in FIG. 2, N IP datagrams 100 are stored in the application data table region 204 along the vertical direction. If the application data table region 204 is not filled with the first through Nth IP datagrams, the application data table region 204 is entirely filled up by filling up the remaining space with zeros, i.e., performing zero padding on the remaining space, as indicated by numeral 208. Once the application data table region 204 is entirely filled with the IP datagrams or by performing the zero padding, R-S encoding is performed in the horizontal direction and parity data resulting from the R-S encoding is filled in an R-S data table region 206, as illustrated in FIG. 2.
By performing R-S encoding with respect to IP datagrams through the MPE-FEC process described with reference to FIGS. 1 and 2, an MPE-FEC frame is formed. Data of the MPE-FEC frame is reconfigured as a transport unit called a section, and the IP datagram 100 is reconfigured as an MPE section with the addition of a section header and Cyclic Redundancy Check (CRC) 32 bits. Parity data resulting from R-S encoding is also reconfigured as an MPE-FEC section with the addition of a section header and CRC 32 bits. The section header includes information required for MPE-FEC processing and time slicing and is positioned in front of a section. The CRC 32 bits are positioned at the rear of a section. These sections are transmitted through a payload of the TS packet 104 over a physical layer.
FIG. 3 explains time slicing for transmission of a TS packet in a transmitter of a general DVB-H system. A general transmitter generally transmits data with a fixed bandwidth as shown by numeral 306, but a transmitter of a DVB-H system transmits a burst of predetermined data as in burst size 310.
The DVB-H system supports time slicing to reduce power consumption of a receiver. Time slicing means data transmission in bursts. In other words, data to be transmitted during the entire time duration 300 is transmitted only during a burst duration 302 by increasing a data rate. Thus, the entire time duration 300 can be divided into the burst duration 302 during which data transmission occurs and an off-time duration 304 during which no data transmission occurs.
In FIG. 3, reference numeral 306 indicates an average bandwidth for general stream transmission without time slicing and reference numeral 308 indicates a burst bandwidth for transmission of the transmitter in the DVB-H system. The entire time duration 300 lasts from the start of current burst transmission until the start of next burst transmission and is divided into the burst duration 302 during which data transmission occurs and the off-time duration 304 during which no data transmission occurs. The burst duration 302 indicates the start and end intervals of burst transmission and the off-time duration 304 during which any transport packet is not transmitted exists between burst durations. A single MPE-FEC frame can be transmitted per burst size 310.
Transmission of an MPE-FEC frame will now be described with reference to FIG. 4. FIG. 4 is a block diagram of a transmitter in a general DVB-H system. The DVB-H system illustrated in FIG. 4 broadcasts IP data as broadcasting data to a plurality of users, together with R-S parity data for error correction of the broadcasting data.
In FIG. 4, an MPE-FEC encoder 401 generates MPE sections including IP datagrams as broadcasting data for section-based transmission of the IP datagrams and generates MPE-FEC sections including parity data for Forward Error Correction (FEC) of the MPE sections. The parity data is generated by a well-known external encoding technique, R-S encoding. The output of the MPE-FEC encoder 401 is delivered to a time slicing processor 403 to undergo time slicing processing for transmission of the broadcasting data in burst. As mentioned above, a single MPE-FEC frame is transmitted during a single burst duration. The IP datagram that undergoes the time slicing processing may be converted into a serial/parallel signal according to a modulation order and a hierarchical or non-hierarchical transmission mode after High Priority (HP) stream processing.
In FIG. 4, a bit interleaver 405 and a symbol interleaver 407 perform bit-based interleaving and symbol-based interleaving to disperse a transmission error, respectively. The interleaved signal is symbol-mapped by a symbol mapper 409 according to a predetermined modulation scheme such as Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM), or 64 QAM and is then delivered to an Inverse Fast Fourier Transform (IFFT) unit 411. The IFFT unit 411 transforms a frequency-domain signal into a time-domain signal. A guard interval insertion unit (not shown) inserts a guard interval into the IFFT transformed signal, thereby generating a base-band Orthogonal Frequency Division Multiplexing (OFDM) symbol. The OFDM symbol is pulse-shaped by a digital base-band filter and undergoes modulation in a Radio Frequency (RF) modulator 413, and is finally transmitted as a TS packet that is a DVB-H signal via an antenna 415.
FIG. 5 illustrates the structure and field format of an MPE section generated by a transmitter of a general DVB-H system. As described with reference to FIGS. 1 and 2, an IP datagram carrying application data 500 is extracted along the vertical direction from the application data table region 204 of the MPE-FEC frame and a section header 502 and CRC 32 bits 504 are added to the application data 500, thereby reconfiguring the application data 500 as an MPE section. Reference numeral 506 indicates the message format of the MPE section including the section header 502, the application data 500 as broadcasting data, and the CRC 32 bits 504. A receiver can recognize that received data is an MPE section by detecting ‘0x3e ’ indicated by reference numeral 508.
Reference numeral 510 indicates a real time parameter and contains frame boundary information indicating a point of time for transmitting the IP datagram to an upper layer when the transmitter transmits an MPE section that does not undergo R-S encoding or recognizes that the receiver normally receives the MPE-FEC frame through CRC checking. The real time parameter 510 is described in detail with reference to FIG. 6.
FIG. 6 illustrates the structure and field format of an MPE-FEC section generated by a transmitter of a general DVB-H system. Parity data (or R-S data) 600 generated through R-S encoding with respect to the MPE section is also reconfigured as an MPE-FEC section 606 with the addition of a section header 602 and CRC 32 bits 604. As discussed above, the header section 602 contains information required for MPE-FEC decoding and time slicing and is positioned in front of a section. The CRC 32 bits 604 are positioned at the rear of a section. These sections are transmitted through a payload of the TS packet 104 over a physical layer.
Reference numeral 606 indicates the message format of the MPE-FEC section including the section header 602, the R-S data 600, and the CRC 32 bits 604. The receiver can recognize that received data is an MPE-FEC section by detecting ‘0x78’ indicated by 608. Reference numeral 610 indicates a real time parameter that will be described in detail with reference FIG. 7.
FIG. 7 illustrates the message format of the real time parameter 510 illustrated in FIG. 5 or the real time parameter 610 illustrated in FIG. 6. Delta_t information 700 indicates a point of time at which transmission of a next MPE-FEC frame starts, i.e., a burst duration, starts. Table_boundary information 702 indicates whether an MPE section generated in a transmitter of a DVB-H system is the last MPE section in an application data table region. When the table_boundary information 702 is set to “1”, it means that a currently transmitted MPE section is the last MPE section of the application data table region in the MPE-FEC frame.
Frame_boundary information 704 indicates whether an MPE-FEC section generated in the transmitter of the DVB-H system is the last MPE-FEC section in the MPE-FEC frame. When the frame_boundary information 704 is set to “1”, it means that a currently transmitted MPE-FEC section is the last MPE-FEC section in the MPE-FEC frame.
FIG. 8 illustrates the physical meaning of the delta-t information 700 included in the real time parameter 600. As described above, the transmitter of the DVB-H system transmits the MPE-FEC frame only during the burst duration 302 using time slicing. Every MPE or MPE-FEC section included in the MPE-FEC frame includes delta-t information 804 in a section header and the delta-t information 804 varies with a section. Thus, a receiver of the DVB_H system stops data reception during the off-time duration 304 to reduce power consumption and resumes the data reception at a next burst start point using the delta_t information 804. To this end, the receiver predicts the next burst start point to resume the data reception by counting during a time interval indicated by the delta-t information 804.
However, if the delta-t information 804 is incorrectly calculated or improperly received due to an error introduced during transmission, the data reception will resume at a wrong point of time, causing a failure to receive desired burst data and thus degrading reception performance.